Display screen or a portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface according to the new design.

The broken line showing of a display screen or portion thereof forms no part of the claimed design. The broken line showing of text and graphical elements forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 